Intrinsic factor mediated cobalamin absorption.

The physiological absorption of vitamin B12 is a complex process which requires the interaction of several macromolecules. Mediated by the glycoprotein, intrinsic factor (IF), this process requires formation of a primary complex between vitamin B12 and IF (IF-B12), the recognition and binding of this complex to specific ileal receptors and the transport of vitamin B12 across the ileal cell. As a measure of this overall process, the vitamin B12 absorption test has helped to identify abnormal vitamin B12 absorption in patients with exocrine pancreatic insufficiency and familial vitamin B12 malabsorption (Immerslung-Grasbeck syndrome). Progress into understanding the role of proteolytic enzymes in promoting vitamin B12 absorption as well as the molecular events of vitamin B12 transport across the ileal cell has been brought about by recent investigation based upon this determination.